Parts of a Tree Background Sheet

Key Words

cambium    chlorophyll    heartwood    lateral    roots    phloem    photosynthesis    sapwood    taproot

Background
Trees are a lot like people. They need food and water, just like you do, to survive and grow. As you read the following, you will learn how trees grow.

Leaves
From skinny pine needles to big palm tree leaves, all tree leaves serve the same purpose: to make food for the tree. Leaves use carbon dioxide from the air, water from the roots, and sunlight to make sugar. This process is called photosynthesis, which takes place with the help of a green pigment in the leaves called chlorophyll which absorbs the sun’s energy. During photosynthesis, the leaves release oxygen which becomes part of the air that we breathe.

Trunk
Just like you depend on your strong bones to give your body structure (without them you would be a mushy pile on the floor), trees have a stiff woody trunk to hold them upright. This trunk acts like a plumbing system to move water (much like your own blood and other body fluids) and food through the tree to help it grow. A trunk has the following parts in it:

1. The outside layer on the trunk is the outer bark. Tree bark can be smooth, scaly, rubbery, flaky, craggy, or bumpy. The outer bark serves the same purpose for trees as skin does for humans, by protecting the tree from injury and disease. Some trees have extra thick bark to protect them from forest fires, while other trees have bad tasting bark to discourage hungry insects.
   
   
2. The layer next to the outer bark is called the inner bark or phloem (FLOW-um). The phloem has lots of little tubes (like your blood vessels) which carry the sticky sugar made by the leaves, called sap, from the leaves to the tree’s branches and trunk.
   
   
3. Next to the phloem is a very thin layer, only one or two cells thick, called the cambium. The cambium is the factory which produces new cells for the other parts of the tree to use. Because of the cambium, the trunk, branches, and roots grow thicker.
   
   
4. The layer next to the cambium is the sapwood. The sapwood is a network of thick cells forming a pipeline. This pipeline carries minerals and water from the roots up to the leaves to help them make food.
   
   
5. Most of the trunk of an old tree is deadwood, called heartwood. The heartwood is old sapwood that no longer transports water and minerals up the tree.

Roots
A tree’s roots are long, underground branches that spread out to help anchor the tree in the soil (so that it does not topple over). Roots also draw up water and nutrients from the soil, just as you might drink soda using a straw. Many trees have a long straight root, called a taproot that reaches down as deep as 15 feet under the ground. They also have roots that branch off to the side, called lateral roots.

Adapted from "Build a Tree", University of Washington's Pack Forest Educator's Guide, 2005